The variance and other measures of line broadening in powder diffractometry. I. Practical considerations

In any attempt to interpret broadened X-ray diffraction peaks in terms of imperfections in polycrystalline specimens, particular attention should be paid to experimental technique and the method of collecting data. The experimental conditions should be arranged to give maximum intensity in as short a time as possible, keeping instrumental effects to a minimum. Of particular importance are the correct choice of receiving slit, incremental change in angle and range of scan for each reflection. All measures of breadth require a knowledge of the background associated with each line, and a reliable estimate of this is given by the variance method. Also with this method, the contribution to the breadth from instrumental effects can be calculated, resulting in a considerable saving in the time taken to accumulate and process the data. Incorrect experimental procedure frequently leads to a false interpretation of diffraction broadening. It is always necessary to obtain data for as many reflections as possible, and desirable to compare the results from different measures of breadth. If a systematic experimental technique has been followed, these should not differ appreciably.